FABP4 inhibited cardiomyocyte contraction with high-affinity EC50 of 0.010 pM and low-affinity EC50 of 0.120 nM, primarily through a calcium-independent pathway.
Does FABP4 or its N-terminal peptide suppress contractility and alter calcium homeostasis in isolated mouse ventricular myocytes?
Full-length FABP4 suppresses cardiomyocyte contractility primarily through a calcium-independent pathway, while its isolated N-terminal domain operates via a distinct calcium-dependent mechanism, highlighting a potential therapeutic target for obesity-related cardiac dysfunction.
Effect estimate: EC50 0.010 pM (high-affinity), EC50 0.120 nM (low-affinity)
Objective Adipocyte Fatty Acid-Binding Protein 4 (FABP4) exerts a direct negative inotropic effect on cardiac muscle, but the underlying cellular mechanisms remain elusive. This study aimed to dissect the specific effects of FABP4 on the contractility and calcium (Ca 2+ ) homeostasis of isolated mouse ventricular myocytes and to characterize the functional role and critical residues of its N-terminal domain. Methods Contractility and intracellular Ca 2+ transients were simultaneously measured in isolated adult mouse ventricular myocytes using an IonOptix system following acute application of recombinant human FABP4 or its synthetic N-terminal peptide (FABP4 aa1-20 ). L-type Ca 2+ current was assessed via the whole-cell patch-clamp technique. Dose-response curves were analyzed using non-linear regression, and site-directed mutagenesis (E15K) was performed to evaluate the functional importance of a key amino acid residue. Results FABP4 inhibited myocyte contraction in a biphasic, dose-dependent manner, with a high-affinity (EC 50 = 0.010 pM) and a low-affinity (EC 50 = 0.120 nM) component. This inhibition was largely independent of Ca 2+ handling, as Ca 2+ transient amplitude was only weakly attenuated at higher concentrations (EC 50 = 0.412 nM), and L-type Ca 2+ current was unaffected. In stark contrast, the FABP4 aa1-20 peptide also inhibited contraction (EC 50 = 0.110 nM) but did so via a Ca 2+ -dependent pathway, robustly suppressing Ca 2+ transients. Mutation of glutamic acid at position 15 (E15K) significantly attenuated the peptide’s inhibitory activity. Conclusion Full-length FABP4 suppresses cardiomyocyte contractility primarily through a Ca 2+ -independent pathway, likely by reducing myofilament Ca 2+ sensitivity. Conversely, its isolated N-terminal domain operates via a distinct, Ca 2+ -dependent mechanism. These findings reveal a complex dual-pathway regulation of cardiac function by FABP4 and identify its N-terminal region as a potential therapeutic target for mitigating obesity-related cardiac dysfunction.
Wang et al. (Tue,) reported a other. Recombinant human FABP4 vs. Control (normal Tyrode's solution) was evaluated on Cardiomyocyte contraction amplitude inhibition (EC50 0.010 pM (high-affinity), EC50 0.120 nM (low-affinity)). FABP4 inhibited cardiomyocyte contraction with high-affinity EC50 of 0.010 pM and low-affinity EC50 of 0.120 nM, primarily through a calcium-independent pathway.